Anvil assembly with snap backup ring

ABSTRACT

An anvil assembly is provided. The anvil assembly includes center rod assembly, a head assembly pivotal relative to the center rod assembly between an operative position and a tilted position, and a mechanism for selectively maintaining the head assembly in the operative position.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Divisional Application of U.S. patentapplication Ser. No. 16/171,498, filed Oct. 26, 2018, which is aContinuation Application which claims that benefit of and priority toU.S. patent application Ser. No. 14/790,105, filed on Jul. 2, 2015, nowU.S. Pat. No. 10,111,668, issued on Oct. 30, 2018, the entire content ofwhich are incorporated herein by reference their entireties.

BACKGROUND Technical Field

The present disclosure relates generally to an anvil assembly having atiltable head which is suitable for use with a circular anastomosisstapler. More specifically, the present disclosure relates a tiltableanvil assembly having an improved retaining mechanism. Background ofRelated Art

Circular anastomosis staplers which include an anvil assembly having atiltable anvil head are known in the art. An example of such circularanastomosis stapler and tiltable anvil assembly are disclosed incommonly owned U.S. Pat. No. 7,364,060 (“the '060 patent”). A furtherexample of a tiltable anvil assembly is disclosed in commonly owned U.S.Pat. No. 8,540,132 (“the '132 patent”). The content of each of the '060patent and the '132 patent are incorporated herein by reference in theirentirety. The anvil assembly described in the '132 patent includes abackup member located within the anvil assembly positioned to preventtilting of the anvil head of the anvil assembly prior to firing of thestapler, e.g., in a proximal position. Upon firing of the stapler, aknife blade of the stapler engages and moves the backup member to aposition, e.g., a distal position, which allows the anvil head to tiltupon retraction of the knife blade. If the backup member sticks to theknife blade upon retraction of the knife blade and/or is otherwise notretained in the distal position, the backup member may return to theproximal position, thereby preventing the anvil head from tilting.

In order to maintain the backup member in the proximal position where itprevents tilting of the anvil head prior to firing, the anvil assemblydescribed in the '132 patent includes a retainer member positioneddistal of the backup member. The retainer member includes a plurality ofdeformable tabs which prevent distal movement of the backup member untila predetermined force sufficient to deform the tabs is applied to thebackup member, i.e., through engagement with the knife blade duringstaple formation. A residual proximal force is produced duringdeformation of the deformable tabs. This force acts on the backup memberwhich may cause the backup member to move proximally towards itsoriginal position. As described in the '132 patent, the tiltingoperation of the anvil assembly relies on the distal positioning of thebackup member following the firing of the stapler. Any proximal forcethat acts on the backup member may cause the backup member to return tothe original proximal position, thereby preventing tilting of the anvilassembly.

Therefore, it would be beneficial to provide an anvil assembly with amechanism or feature for retaining the backup member in the proximalposition prior to firing of the stapling assembly, that allows thebackup member to move to the distal position during firing of thestapling assembly, and that retains the backup member in the distalposition after firing of the stapling assembly such that the anvilassembly may tilt.

SUMMARY

Accordingly, an anvil assembly is provided. The anvil assembly includesa center rod assembly and a head assembly pivotally supported on thecenter rod assembly between an operative position and a tilted position.The head assembly includes a housing, a post extending proximally fromthe housing and defining a proximal annular groove, and a backup memberoperably supported about the post, wherein the backup member is movablefrom a first position in which a portion of the backup member ispositioned to prevent pivotal movement of the head assembly from theoperative position to the tilted position, to a second position in whichthe backup member is positioned to permit pivotal movement of the headassembly from the operative position to a tilted position. The backupmember includes a first locking feature and a second locking featurereceivable within the proximal annular groove of the post to maintainthe backup member in the first position.

In embodiments, the post further defines a distal annular groove, thefirst and second locking features being received within the distalannular groove to maintain the backup member in the second position. Thecenter rod assembly may include a center rod having at least one tab.The at least one tab may engage the backup member when the backup memberis in the first position to maintain the head assembly in the operativeposition. Movement of the backup member from the first position to thesecond position may disengage the backup member from the at least onetab to permit the head assembly to move to the tilted position.

The first and second locking features may be configured to preventmovement of the backup member from the first position to the secondposition until a predetermined force has been applied to the backupmember. The first and second locking features may be configured to flexradially outward when the predetermined force is applied to the backupmember. The first and second locking features may each include a ridgeconfigured for receipt within the proximal annular groove when thebackup member is in the first position and within the distal annulargroove when the backup member is in the second position.

In embodiments, an anvil assembly in accordance with the presentdisclosure includes a center rod assembly, and a head assembly pivotallysupported on the center rod assembly between an operative position and atilted position. The head assembly includes a housing, a post extendingproximally from the housing, and a backup member operably supportedabout the post, wherein the backup member is movable from a firstposition in which a portion of the backup member is positioned toprevent pivotal movement of the head assembly from the operativeposition to the tilted position, to a second position in which thebackup member is positioned to permit pivotal movement of the headassembly from a operative position to the tilted position. The backupmember includes a first detent and a second detent configured to engagea proximal surface of the post to maintain the backup member in thefirst position.

In embodiments, the post defines first and second cutouts for receivingthe respective first and second detents when the backup member is in thesecond position. The center rod assembly may include a center rod havingat least one tab, wherein the at least one tab engages the backup memberwhen the backup member is in the first position to maintain the headassembly in the operative position. Movement of the backup member fromthe first position to the second position may disengage the backupmember from the at least one tab to permit the head assembly to move tothe tilted position. The at least one tab may engage one of the firstand second detents. The first and second detents may be configured toprevent movement of the backup member from the first position to thesecond position until a predetermined force has been applied to thebackup member.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the presently disclosed anvil assembly aredisclosed herein with reference to the drawings wherein:

FIG. 1 is a perspective side view of a surgical stapling deviceincluding an embodiment of an anvil assembly according to the presentdisclosure;

FIG. 2 is enlarged view of the indicated area of detail shown in FIG. 1;

FIG. 3 is a cross-sectional side view taken along line 3-3 shown in FIG.2 , illustrating the anvil assembly approximated against a loading unit;

FIG. 4 is a perspective side view of the anvil assembly shown in FIG. 1with the parts separated;

FIG. 5 is a perspective side view of a backup member of the anvilassembly shown in FIG. 4 ;

FIG. 6 is a perspective side view of the anvil assembly shown in FIG. 4;

FIG. 7 is an enlarged view of the indicated area of detail shown in FIG.6 ;

FIG. 8 is a cross-sectional perspective view taken along line 8-8 shownin FIG. 7 ;

FIG. 9 is a cross-sectional side view taken along line 9-9 shown in FIG.7 ;

FIG. 10 is a cross-sectional side view taken along line 3-3 shown inFIG. 2 , during a tissue cutting stroke;

FIG. 11 is a perspective top view of a head assembly of the anvilassembly shown in FIG. 4 subsequent to firing of the surgical staplingdevice show in FIG. 1 ;

FIG. 12 is a cross-sectional perspective view taken along line 8-8 shownin FIG. 7 subsequent to tilting of the head assembly;

FIG. 13 is a cross-sectional side view taken along line 9-9 shown inFIG. 7 , subsequent to tilting of the head assembly;

FIG. 14 is a perspective view of another embodiment of an anvil assemblyaccording to the present disclosure;

FIG. 15 is an enlarged perspective view a head assembly of the anvilassembly shown in FIG. 14 with a cutting ring removed and a backupmember in a proximal position;

FIG. 16 is an enlarged view of the indicated area of detail shown inFIG. 15 ;

FIG. 17 is an enlarged perspective view of the head assembly of theanvil assembly shown in FIG. 14 with the backup member in a distalposition; and

FIG. 18 is a perspective side view of the anvil assembly shown in FIG.14 with the head assembly in a tilted position and the backup member andthe cutting ring removed.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the presently disclosed anvil assembly will now bedescribed in detail with reference to the drawings in which likereference numerals designate identical or corresponding elements in eachof the several views. As is common in the art, the term “proximal”refers to that part or component closer to the user or operator, i.e.surgeon or clinician, while the term “distal” refers to that part orcomponent further away from the user.

Referring initially to FIGS. 1-3 , an anvil assembly according to anembodiment of the present disclosure, shown generally as anvil assembly100, is secured to a surgical stapling device 10. The surgical staplingdevice 10 includes a powered handle 20, an adapter assembly 30, anextension assembly 40, and a loading unit 50. Although shown anddescribed with reference to anvil assembly 100 and surgical staplingdevice 10, the aspects of the present disclosure may be modified for usewith anvil assemblies having alternative configurations, with manualsurgical stapling devices having various configurations, and withpowered surgical stapling devices having alternative configurations. Fora detailed description of an exemplary surgical stapling device, pleaserefer to commonly owned U.S. Pat. No. 9,023,014 (“the '014 patent) andU.S. Pat. Appl. Publ. No. 2012/0253329 (“the '329 application”), thecontents of which are incorporated by reference herein in theirentirety.

Referring to FIGS. 2-4 , briefly, the anvil assembly 100 includes a headassembly 112 pivotally secured to a center rod assembly 114. The headassembly 112 includes a housing 120, a post 130, a backup member 140,and a cutting ring 150. The center rod assembly 114 includes a centerrod 160 and a biasing mechanism 170 (FIG. 3 ) operably received within adistal bore 161 (FIG. 3 ) of the center rod 160. The biasing mechanism170 facilitates moving of the head assembly 112 relative to the centerrod 160 between at least an operative position (FIG. 6 ) and a tiltedposition (FIG. 11 ). The biasing mechanism 170 includes a plunger member172 (FIG. 3 ) and a biasing member, e.g., a compression spring 174 (FIG.3 ). For a detailed description of an exemplary center rod assembly 114,please refer to the '132 patent, the contents of which were previouslyincorporated by reference herein.

With continued reference to FIGS. 3 and 4 , the housing 120 of the headassembly 112 of the anvil assembly 100 defines a plurality of stapleforming pockets 121 on a proximal facing surface 122 thereof.Alternatively, the head assembly 112 may include an anvil plate (notshown), defining a plurality of staple forming pockets (not shown),supported on the proximal facing surface 122 of the housing 120. Thehousing 120 further defines a cavity 123 between an inner wall 124 andthe post 130 for operably receiving the backup member 140 and thecutting ring 150. As will be described in further detail below, theinner wall 124 of the housing 120 defines an annular groove 125 forreceiving a plurality of tabs 156 of the cutting ring 150.

As shown, the post 130 of the head assembly 112 is monolithically formedwith and centrally positioned within the housing 120. Alternately, thehousing 120 and the post 130 are formed separately and fastened togetherusing a known fastening technique, e.g., adhesive, welding, frictionfit, etc. The post 130 includes a substantially cylindrical body 132having a projection 134, and defining opposed cutouts 133 and proximaland distal annular grooves 135 a, 135 b. The projection 134 of the post130 defines a throughbore 131 and is configured to operably engage thecenter rod 160 of the center rod assembly 114. More particularly, theprojection 134 of post 130 is received between extensions 162 of thecenter rod 160 of the center rod assembly 114 and is pivotally securedto the center rod 160 by a pivot pin 162 received through thethroughbore 131.

With additional reference to FIG. 5 , the backup member 140 of the headassembly 112 includes an annular body 142 and an annular flange 144extending from the annular body 142. The backup member 140 defines anannular groove 141 disposed between the annular body 142 and the annularflange 144, and a central opening 143 extending through the annular body142 and the annular flange 144. The backup member 140 is operablyreceivable within the cavity 123 of the housing 120 of the head assembly112 about the post 130. The backup member 140 includes opposedprotrusions 146 extending within the central opening 143 and receivablewithin the opposed cutouts 133 of the post 130 when the backup member140 is received within the cavity 123 of the housing 120. As will bedescribed in further detail below, when the backup member 140 is in aproximal position (FIG. 3 ), the opposed protrusions 146 engage tabs 162a formed on the extensions 162 of the center rod 160 of the center rodassembly 114 to maintain the head assembly 112 in an operative position(FIG. 3 ).

With particular reference still to FIG. 5 , the backup member 140further includes opposed locking features 148 that frictionally engagethe post 130 when the backup member 140 is received within the cavity121 of the housing 120 and about the post 130. More particularly, eachof the opposed locking features 148 forms a resilient member thatincludes a ridge 148 a selectively receivable within the proximal anddistal annular grooves 135 a, 135 b of the post 130. When the ridges 148a of the opposed locking features 148 of the backup member 140 arereceived within the proximal annular groove 135 a of the post 130, theopposed locking features 148 operate to maintain the backup member 140in the proximal position (FIG. 3 ). Although shown including two lockingfeatures 148, it is envisioned that the backup member 140 may includethree (3) or more locking features 148.

When a predetermined force is applied to the backup member 140 in thedistal direction, the opposed locking features 148 of the backup member140 are configured to flex radially outwardly as the backup member 140moves in a distal direction. The radial outward flexion of the ridges148 a of the opposed locking features 148 retract the ridges 148 a fromwithin the proximal annular groove 135 a, thereby permitting continueddistal movement of the backup member 140. The distal annular groove 135b of the post 130 is positioned such that when the backup member 140 ismoved to the distal position (FIG. 13 ), the ridges 148 a of the opposedlocking features 148 align with and are subsequently received within thedistal annular groove 135 b because of the resilient nature of theopposed locking features 148.

With continued reference to FIGS. 3 and 4 , the cutting ring 150 of thehead assembly 112 of the anvil assembly 100 includes an annular body 152and defines an annular groove 151 and a central opening 153. The cuttingring 150 is secured about the annular flange 144 of the backup member140 and includes an inwardly extending lip 154 that is received withinthe annular groove 143 of the backup member 140 for securing the cuttingring 150 to the backup member 140. As noted above, a plurality of tabs156 extend outwardly from the annular body 152 of the cutting ring 150.The plurality of tabs 156 are received within the annular groove 125formed in the inner wall 124 of the housing 120 when the cutting ring150 is received within the cavity 123 of the housing 120. The pluralityof tabs 156 maintains the backup member 140 and the cutting ring 150within the housing 120 of the head assembly 112.

Although the cutting ring 150 is shown and described as being formed asan independent component that is secured to the backup member 140 byplacing the cutting ring 150 around the annular flange 144 of the backupmember 140 and receiving the lip 154 of the cutting ring 150 within theannular groove 143 of the backup member 140, it is envisioned that thebackup member 140 and the cutting ring 150 may be integrally formed, orformed as a one piece or monolithic structure.

With reference now to FIGS. 6-9 , the anvil assembly 100 is shown withthe head assembly 112 in the operative position. In the operativeposition, the backup member 140 and the cutting ring 150 are in theproximal position. When the backup member 140 and the cutting ring 150are in the proximal position, the ridges 148 a of the opposed lockingfeatures 148 of the backup member 140 are received within the proximalannular groove 135 a of the post 130 to maintain the backup member 140and the cutting ring 150 in the proximal position. Additionally, theplurality of tabs 156 (FIG. 8 ) of the cutting ring 150 are receivedwithin the annular groove 125 formed in the inner surface 124 of thehousing 120 to maintain the backup member 140 and the cutting ring 150within the cavity 123 of the housing 120.

As noted above, the head assembly 112 of the anvil assembly 100 ismaintained in the operative position by the backup member 140 when thebackup member 140 is in the proximal position. In particular, theopposed protrusions 146 of the backup member 140 engage the tabs 162 aextending from the extension 162 of the center rod 160 of the center rodassembly 114 to prevent the head assembly 112 from pivoting to thetilted position (FIG. 11 ) relative to the center rod 160.

With reference now to FIG. 10 , during actuation of surgical staplingdevice 10, subsequent to the stapling of tissue in a two stroke staplingdevice, or concurrently with the stapling of tissue in a single strokedevice, the knife 52 of the loading unit 50 is advanced into contactwith the cutting ring 150 of the head assembly 112 of the anvil assembly100. Since the cutting ring 150 is secured to the backup member 140, theforce applied to the cutting ring 150 is transferred to the backupmember 150. As noted above, when the predetermined force is applied tothe backup member 140, the opposed locking features 148 of the backupmember 140 flex radially outwardly to retract the ridges 148 a of theopposed locking features 148 from within the proximal annular groove 135a of the post 130 to allow the backup member 140 to move relative to thepost 130.

Turning now to FIGS. 11-13 , the anvil assembly 100 is shown with thebackup member 140 and the cutting ring 150 in the distal position. Asthe backup member 140 moves to the distal position, the opposedprotrusions 144 of the backup member 140 disengage from the tabs 162 aformed on the extensions 162 of the center rod 160 of the center rodassembly 114 to permit the head assembly 112 to pivot relative to thecenter rod assembly 114. As noted above, when the backup member 140 isin the distal position, the ridges 148 a of the opposed locking features148 align with and are received within the distal annular groove 135 bof the post 130 to lock the backup member 140 in the distal position.

It is noted that the anvil head assembly 100 will not immediately tiltor pivot to the tilted position upon firing of the surgical staplingdevice 10 because, upon firing, the head assembly 100 is in anapproximated position, i.e., the head assembly 100 is in close alignmentwith the loading unit 50 of the surgical stapling device 10 (FIG. 10 ).As such, the head assembly 100 is prevented from tilting until the headassembly 112 is moved away from the loading unit 50.

With reference to FIGS. 14-18 , another embodiment of an anvil assemblyaccording to the present disclosure is shown generally as anvil assembly200. The anvil assembly 200 is substantially similar to the anvilassembly 100 described hereinabove and will only be described in detailas relates to the differences therebetween.

The anvil assembly 200 includes a head assembly 212 and a center rodassembly 214. The head assembly 212 includes a housing 220, a post 230,a backup member 240, and a cutting ring 250. The center rod assemblyincludes a center rod 260 and a biasing assembly 270 (FIG. 18 ). Thehousing 220 is substantially similar to housing 120 and will not bedescribed any further herein.

The post 230 of the head assembly 212 is centrally disposed within thehousing 220 and includes a substantially cylindrical body 232. Aprojection 234 extends proximally from the cylindrical body 232 and ispivotally secured to extensions 262 of the center rod 260. Thecylindrical body 232 of the post 230 defines opposed cutouts 233. Aswill be described in further detail below, the opposed cutouts 233facilitate securing the backup member 240 in a distal position (FIG. 17).

The backup member 240 includes a substantially planar body 242 and anannular flange 244 extending proximally from the planar body 242. Theannular flange 244 is receivable about the post 230 and includes opposeddetents 246 formed on a proximal end of the annular flange 244. Theopposed detents 246 operate to maintain the backup member 240 in theproximal position prior to actuation of the surgical stapler 10 (FIG. 1) and in the distal position subsequent to actuation of the surgicalstapler 10. The opposed detents 246 further operate to maintain the headassembly 212 in the operative position when the backup member 240 is inthe proximal position. Although shown including two detents 246, it isenvisioned that the backup member 140 may include three (3) or moredetents 246.

The backup member 240 includes a plurality of tangs 248 for securing thecutting ring 250 to the backup member 240. Although shown including aplurality of tangs 248, it is envisioned that the cutting ring 250 maybe secured to the backup member 240 in any suitable manner. The cuttingring 250 is substantially similar to the cutting ring 150 describedhereinabove and will not be described in further detail herein.

With reference to FIGS. 14-16 , when the backup member 240 is in theproximal position, a distal portion 246 b of the opposed detents 246engages a top surface 232 a (FIG. 16 ) of the cylindrical body 232 ofthe post 230 to maintain the backup member 240 in the proximal position.When the backup member 240 is in the proximal position, the opposeddetents 246 are aligned with the tabs 262 a formed on the extension 262of the center rod 260 of the center rod assembly 214 to maintain thehead assembly 212 in the operative position.

When a predetermined force is applied to the backup member 240, e.g., byknife 52 (FIG. 10 ) during actuation of the surgical stapler 10, theopposed detents 246 flex radially outwardly as the backup member 240moves distally about the cylindrical body 232 of the post 230 to permitmovement of the backup member 240 to the distal position. The post 230may include a longitudinal slot (not shown) for receiving the detents246 and facilitating distal movement of the backup member 240 from theproximal position to the distal position.

When the backup member 240 is in the distal position, the opposeddetents 246 of the backup member 240 are received within the opposedcutout 233 of the post 230 to secure the backup member 240 in the distalposition. More particularly, a proximal surface 246 a of the opposeddetents 246 engages the cylindrical body 232 of the post 230 when thedetents 246 are received in the cutouts 233 of the post 230 to maintainthe backup member 240 in the distal position.

Persons skilled in the art will understand that the devices and methodsspecifically described herein and illustrated in the accompanyingdrawings are non-limiting exemplary embodiments. It is envisioned thatthe elements and features illustrated or described in connection withone exemplary embodiment may be combined with the elements and featuresof another without departing from the scope of the present disclosure.As well, one skilled in the art will appreciate further features andadvantages of the disclosure based on the above-described embodiments.Accordingly, the disclosure is not to be limited by what has beenparticularly shown and described, except as indicated by the appendedclaims.

What is claimed is:
 1. An anvil assembly comprising: a center rodassembly including a center rod having at least one tab; and a headassembly pivotally supported on the center rod assembly and moveablebetween an operative position and a tilted position, the head assemblyincluding: a housing; a post extending proximally from the housing; anda backup member operably supported about the post, wherein the backupmember is movable from a first position in which a portion of the backupmember is positioned to prevent pivotal movement of the head assemblyfrom the operative position to the tilted position, to a second positionin which the backup member is positioned to permit pivotal movement ofthe head assembly from the operative position to the tilted position,the backup member including at least one detent configured to engage aproximal surface of the post to maintain the backup member in the firstposition, wherein the at least one tab engages the backup member whenthe backup member is in the first position to maintain the head assemblyin the operative position.
 2. The anvil assembly according to claim 1,wherein the post defines at least a first cutout for receiving the atleast one detent when the backup member is in the second position. 3.The anvil assembly according to claim 1, wherein movement of the backupmember from the first position to the second position disengages thebackup member from the at least one tab to permit the head assembly tomove to the tilted position.
 4. The anvil assembly according to claim 1,wherein the at least one tab engages the at least first detent.
 5. Theanvil assembly according to claim 1, wherein the at least one detent isconfigured to prevent movement of the backup member from the firstposition to the second position until a predetermined force is appliedto the backup member.
 6. The anvil assembly according to claim 1,wherein the at least one tab includes first and second tabs, and the atleast one detent includes first and second detents.
 7. The anvilassembly according to claim 1, wherein the post includes a top surfaceand the at least one detent includes a distal portion, the distalportion of the at least one detent engaging the top surface of the postwhen the backup member is in the first position to maintain the backupmember in the first position.
 8. An anvil assembly comprising: a centerrod assembly including a center rod having at least one tab; and a headassembly pivotally supported on the center rod assembly and moveablebetween an operative position and a tilted position, the head assemblyincluding: a housing; a post extending proximally from the housing; anda backup member operably supported about the post, wherein the backupmember is movable from a first position in which a portion of the backupmember is positioned to prevent pivotal movement of the head assemblyfrom the operative position to the tilted position, to a second positionin which the backup member is positioned to permit pivotal movement ofthe head assembly from the operative position to the tilted position,the backup member including at least one detent configured to engage aproximal surface of the post to maintain the backup member in the firstposition, wherein the at least one detent engages the post when thebackup member is in the first position to maintain the backup member inthe first position.
 9. The anvil assembly according to claim 8, whereinthe post defines at least a first cutout for receiving the at least onedetent when the backup member is in the second position.
 10. The anvilassembly according to claim 8, wherein movement of the backup memberfrom the first position to the second position disengages the backupmember from the at least one tab to permit the head assembly to move tothe tilted position.
 11. The anvil assembly according to claim 8,wherein the at least one tab engages the at least one detent.
 12. Theanvil assembly according to claim 8, wherein the at least one detent isconfigured to prevent movement of the backup member from the firstposition to the second position until a predetermined force is appliedto the backup member.
 13. The anvil assembly according to claim 8,wherein the at least one tab includes first and second tabs, and the atleast one detent includes first and second detents.
 14. The anvilassembly according to claim 8, wherein the post includes a top surfaceand the at least one detent includes a distal portion, the distalportion of the at least one detent engaging the top surface of the postwhen the backup member is in the first position to maintain the backupmember in the first position.
 15. A surgical stapling device comprising:an actuation assembly including a trocar member; and an anvil assemblyreleasably securable to the trocar member, the anvil assembly including:a center rod assembly including a center rod having at least one tab;and a head assembly pivotally supported on the center rod assembly andmoveable between an operative position and a tilted position, the headassembly including: a housing; a post extending proximally from thehousing; and a backup member operably supported about the post, whereinthe backup member is movable from a first position in which a portion ofthe backup member is positioned to prevent pivotal movement of the headassembly from the operative position to the tilted position, to a secondposition in which the backup member is positioned to permit pivotalmovement of the head assembly from the operative position to the tiltedposition, the backup member including at least one detent configured toengage a proximal surface of the post to maintain the backup member inthe first position, wherein the at least one tab engages the backupmember when the backup member is in the first position to maintain thehead assembly in the operative position.
 16. The surgical staplingdevice according to claim 8, wherein the post defines at least a firstcutout for receiving the at least one detent when the backup member isin the second position.
 17. The surgical stapling device according toclaim 15, wherein movement of the backup member from the first positionto the second position disengages the backup member from the at leastone tab to permit the head assembly to move to the tilted position. 18.The surgical stapling device according to claim 15, wherein the at leastone tab engages the at least one detent.
 19. The surgical staplingdevice according to claim 15, wherein the at least one detent isconfigured to prevent movement of the backup member from the firstposition to the second position until a predetermined force is appliedto the backup member.
 20. The surgical stapling device according toclaim 15, wherein the at least one tab includes first and second tabs,and the at least one detent includes first and second detents.